The invention relates to the art of pad transfer printing, and more particularly to an improved doctor blade for use in such printing.
In pad transfer printing generally, a cliche is used, the cliche having an image recessed in the normally planar working surface, typically in the form of a pattern of closely spaced discrete recesses. The working surface is flooded with a thixotropic ink, some of which flows into and fills the discrete recesses. A doctor blade then is passed over the working surface, Shearing the excess ink not in the recesses and removing it from the working surface. A resilient pad is then lowered into contact with the image, whereupon the ink in the recesses transfers to the pad. The pad is then pressed against the final destination target, such as a golf ball or coffee mug, resulting of a transferral of the image to the target.
Early processes of this general type used a cliche made of stainless steel having the image etched or otherwise formed in the working surface. Such processes were generally satisfactory from the standpoint of service life of the cliche, but the cost 0f making the cliche were substantial.
Note recently, much less expensive cliches have become available. These more recent cliches are in the form of certain photopolymer films which are somewhat soluble in water. If a portion of such a film is exposed to ultraviolet radiation, that portion becomes less soluble in water. Accordingly, an opaque image placed on the upper or working surface of the film protects the polymer in the regions under the image from the radiation, leaving it soluble. A subsequent water bath then removes the polymer which had been protected by the image, leaving a recessed copy of the image ready to receive the ink. The opposite or lower surface of the film is typically affixed by an adhesive to a supporting substrate. Typical commercially available polymer films of this type are "PRINTIGHT" from Toyobo and "LSL-295-B" from TOK. Cliches made by such processes are far less expensive than the stainless steel cliches.
The known prior art practice is to use various types of rigid doctor blades with these photopolymer cliches, as was common with the stainless steel cliches.
Unfortunately, this results in short service lives for the cliches, which become damaged after perhaps 1-2000 cycles of use, with a certain percentage of premature failure.
These and other problems with the prior art practices are avoided by the present invention, which provides an improved doctor blade permitting substantially improved service life for the cliches with a lower percentage of premature failures.